Add --completions

Cargo.toml

@@ -37,6 +37,7 @@ tracing-subscriber = "0.3"
 walkdir = "2.3"
 whoami = "1.2"
 clap = { version = "3.2.17", features = ["derive"] }
+clap_complete = "3.2.5"
 
 [dependencies.cp_r]
 version = "0.5.1"

NEWS.md

@@ -2,6 +2,8 @@
 
 ## UNRELEASED
 
+- New: `cargo mutants --completions` to generate shell completions using `clap_complete`.
+
 - Changed: Since `cargo-mutants` now sets `RUSTFLAGS` to avoid false failures from warnings, it is unlikely to match the existing build products in the source directory `target/`, and in fact building there is just likely to cause rebuilds in the source. So, `cargo mutants` now never builds in the source directory, and never copies `target/`. The behavior now is as if `--no-copy-target` was always passed. That option is still accepted, but it has no effect.
 
 - Changed: Find mutants before doing a baseline test, so that you will find out earlier if there's nothing to test.

README.md

@@ -21,6 +21,14 @@ the tests really check the code's behavior.
 cargo install cargo-mutants
 ```
 
+To install shell completions run for example:
+
+```sh
+cargo mutants --completions fish >~/.config/fish/completions/cargo-mutants.fish
+```
+
+```sh
+
 ## Using cargo-mutants
 
 Just run `cargo mutants` in a Rust source directory, and it will point out

src/main.rs

@@ -29,7 +29,9 @@ use std::time::Duration;
 use anyhow::Result;
 use camino::Utf8Path;
 use camino::Utf8PathBuf;
+use clap::CommandFactory;
 use clap::Parser;
+use clap_complete::{generate, Shell};
 use path_slash::PathExt;
 use serde_json::json;
 use serde_json::Value;
@@ -79,6 +81,10 @@ struct Args {
     #[clap(long)]
     check: bool,
 
+    /// generate autocompletions for the given shell.
+    #[clap(long)]
+    completions: Option<Shell>,
+
     /// show the mutation diffs.
     #[clap(long)]
     diff: bool,
@@ -174,6 +180,8 @@ fn main() -> Result<()> {
     interrupt::install_handler();
     if args.version {
         println!("{} {}", NAME, VERSION);
+    } else if let Some(shell) = args.completions {
+        generate(shell, &mut Cargo::command(), "cargo", &mut io::stdout());
     } else if args.list_files {
         if args.json {
             list_files_as_json(&source_tree, &options)?;

tests/cli.rs

@@ -1172,3 +1172,22 @@ fn check_text_list_output(dir: &Path, test_name: &str) {
         insta::assert_snapshot!(format!("{test_name}__{name}.txt"), content);
     }
 }
+
+/// `cargo mutants --completions SHELL` produces a shell script for some
+/// well-known shells.
+///
+/// We won't check the content but let's just make sure that it succeeds
+/// and produces some non-empty output.
+#[test]
+fn completions_option_generates_something() {
+    for shell in ["bash", "fish", "zsh", "powershell"] {
+        println!("completions for {shell}");
+        run_assert_cmd()
+            .arg("mutants")
+            .arg("--completions")
+            .arg(shell)
+            .assert()
+            .success()
+            .stdout(predicate::str::is_empty().not());
+    }
+}